Bibliographic Information

"Heat Capacity of MgSiN₂ Between 8 and 800 K," R.J. Bruls, H.T. Hintzen, R. Metselaar, and J.C. van Miltenburg, Journal of Physical Chemistry B, Vol. 102, pp. 7871-7876 (1998), published by American Chemical Society.

General Materials Processing Notes

The authors cite W.A. Groen et al., J. Eur. Ceram. Soc., Vol. 12, 413 (1993), R.J. Bruls et al., J. Mater. Sci., Vol. 34, 4519 (1999), and H.T. Hintzen et al., J. Mater. Sci. Lett., Vol. 13, 1314 (1994), and summarize the procedure as follows. "MgSiN₂ is a ternary adamantine type compound with tetrahedral coordination of Mg and Si. It can be deduced from the well-known AlN by systematically replacing two Al ions with one Mg and one Si ion. ... For the (8 K to 400 K) measurement, isostatically pressed MgSiN₂ powder pellets were used. ... The major phase impurity in the MgSiN₂ sample was MgO as a secondary phase. The (mass fraction) impurity content of the MgSiN₂ sample was estimated to be less than 1.0% on the basis of the measured oxygen content and the measured X-ray diffraction pattern of the sample. ... The tablet (for 300 K to 800 K) was prepared by hot uniaxial pressing. ... Nearly single phase, glassy phase free, fully dense MgSiN₂ ceramics with an isotropic microstructure were obtained. ... The major phase impurity in the MgSiN₂ ceramic sample was MgO as a secondary phase. The (mass fraction) impurity content... was estimated to be less than 2.0% on the basis of the measured oxygen content and the measured X-ray diffraction pattern of the sample."

Measurement Methods

The authors cite J.C. van Miltenburg et al., J. Chem. Thermodyn., Vol. 19, 1129 (1987), and summarize the procedure as follows. "The specific heat at constant pressure (C_p) for MgSiN₂ in the range of 8 K - 400 K was measured with an adiabatic calorimeter. ... Isostatically pressed powder pellets (diameter, 6.5 mm; thickness, 1 mm - 2 mm) with a total mass of about 12.12 g were put into a sample holder (copper vessel) with a mass of about 20 g and an internal volume of about 11 cm³. Before sealing the copper vessel, it was evacuated and filled with 1000 Pa of He gas as a heat exchanger. The sample plus sample holder was heated to the highest measuring temperature, before starting the C_p measurement, to enhance possible energy relaxation. Subsequently, the sample plus sample holder was cooled to the lowest measuring temperature. Then, stepwise, a known quantity of energy was added to the sample plus sample holder, and the temperature increase was measured. The temperature was measured with a Pt resistance thermometer (100 Ω at 298.15 K, Oxford instruments) with an accuracy of ±0.003 K between 5 K and 30 K and ±0.005 K above 30 K. ... From the temperature increase and the amount of energy added, the specific heat of the sample plus the sample holder was calculated. Another independent specific heat measurement of the empty sample holder was used to correct for the specific heat of (the holder) and subsequently to determine the specific heat of the MgSiN₂ sample. ... the reliability of the measured adiabatic calorimeter data was estimated to deviate no more than 1% from the true values... For the differential scanning calorimeter (DSC) measurement MgSiN₂ ceramic disks (diameter, 4.90 mm; thickness, 1.6 mm - 1.8 mm) were used cut from a sintered MgSiN₂ tablet. ... The C_p of the ceramic samples in the range of 300 K - 800 K was measured with a DSC Setaram 111. ...measurements were performed under a nitrogen atmosphere using a heating rate of 10 K min^-1. ... Sapphire rods (Calorimeter Conference Sample 720), supplied by the National Institute of Standards and Technology (NIST), were used as a reference material. The mass of the MgSiN₂ sample was 0.38659 g, and the mass of the sapphire reference material was 0.19497 g. ... the reliability of the measured DSC data was estimated to deviate no more than 3% from the true values... values between 0 K and 8 K were obtained by extrapolation using the... data between 16 K and 24 K and the Debye theory of the specific heat."

Index of Materials and Properties